- Email: [email protected]
State of the art of electronic personal dosimeters for neutrons
Nuclear Instruments and Methods in Physics Research A 505 (2003) 411–414
State of the art of electronic personal dosimeters for neutrons Francesco d’Erricoa,b,*, Marlies Luszik-Bhadrac, Thierry Lahayed a
Department of Therapeutic Radiology, Yale University School of Medicine, P.O. Box 208040, New Haven, CT 06520-8040, USA Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione (DIMNP), Universita" degli Studi di Pisa, Via Diotisalvi 2, I-56126 Pisa, Italy c Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, D-38116 Braunschweig, Germany d Institute for Protection and Nuclear Safety (IRSN), F 92265 Fontenay aux Roses Cedex, France
b
Abstract Despite a widely recognised need, electronic devices for personal dosimetry of neutrons or mixed neutron–photon fields are still far less established than systems for photon or beta radiations. A large research project is in progress to evaluate different methods currently used or under development for electronic personal dosimetry in mixed neutron– photon fields. The study includes testing in calibration fields as well as in representative workplaces of the nuclear industry. This paper describes the commercial and laboratory systems under investigation and their response characteristics. These were determined so far with measurements using ISO standard monoenergetic beams up to 19 MeV at the PTB in Braunschweig, Germany. r 2003 Published by Elsevier Science B.V. PACS: 87.53.PQ; 87.50.NP Keywords: Electronic personal dosimeters; monoenergetic neutron fields; Dose equivalent
1. Introduction A large number of electronic personal dosimeters for photon/beta radiations have been commercially available for several years and are currently being considered for primary dosimetry thanks to their high level of accuracy and reliability coupled with low detection limits. Conversely, electronic devices for personal dosimetry of neutrons or mixed neutron–photon fields
*Corresponding author. Department of Therapeutic Radiology, Yale University School of Medicine, P.O. Box 208040, New Haven, CT 06520-8040, USA. Tel.: +1-203-785-6679; fax: +1-203-737-4252. E-mail address: [email protected] (F. d’Errico).
are still far less established, despite a need which is widely recognised. In fact, increasing exposure levels are reported in the nuclear industry, deriving from more frequent in-service entries at commercial nuclear power plants, and from increased plant decommissioning and refurbishment activities. In addition, specific neutron exposures are increasing due to higher-burn up of fuel and to the use of mixed oxide elements. In recent years, a series of consensus requirements for neutron sensitive electronic personal dosimeters have been developed, mainly based on ICRP Publication 60 [1]. In particular, it has been suggested that the lower detection level should be 10 mSv (10 mSv/h, in ratemeter mode), dose increments should be in tens of microsievert, and the
0168-9002/03/$ - see front matter r 2003 Published by Elsevier Science B.V. doi:10.1016/S0168-9002(03)01110-0
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F. d’Errico et al. / Nuclear Instruments and Methods in Physics Research A 505 (2003) 411–414
overall uncertainly on dose equivalent readings should not exceed a factor of 2 in any neutron spectrum [2–4]. In addition, criticality accidents such as the recent one in Tokai Mura, Japan, and a sustained military interest are behind the requirement that neutron EPDs should be capable of measuring high doses within short times [5], e.g., several Sievert per minute. More general requirements have also been expressed, such as availability of alarm functions, direct read out, computer interface, integration in monitoredaccess systems, battery charge allowing 100 h of continuous use and weight below 200 g. Addressing this demand, some neutron EPDs have appeared on the market in recent years. However, their development is a very difficult task, mainly because their physics, i.e. neutron interactions with matter, is much more complex than for photons and because a strongly variable energydependent quality factor must be folded into the detector response. In this framework, a research project sponsored by the European Commission has started to evaluate the relative merits of different methods for electronic personal dosimetry in mixed neutron–photon fields. The project includes investigations in standard calibration fields as well as in representative workplaces of the nuclear industry. This manuscript summarises the main characteristics of the commercial and laboratory systems under investigation and describes the dose equivalent response functions determined so far with measurements in reference neutron fields.
2. Materials and methods Three fundamental approaches can be identified for neutron electronic personal dosimetry. These
are based on: (a) using a physical or (bio)chemical effect with properties similar to the deposition of dose equivalent in tissue, (b) measuring LET spectra and folding them over the quality factor, and (c) designing a device with an energy dependence of the response resembling the fluence-to-dose equivalent conversion coefficient, hF ðEÞ: Most neutron EPDs, virtually all commercial ones, are based on the last method. However, two of the laboratory devices discussed hereafter follow the first two approaches. The commercial electronic personal dosimeters investigated in this work were: Aloka PDM-313, Fuji Electric EPD (NRN), Saphydose-n and Siemens EPD-N. Their main published characteristics are reported in Table 1. These devices are all based on semiconductor detectors, which are particularly attractive because of their ruggedness, small dimensions and limited cost. However, their use in neutron dosimetry poses two main problems: energy dependence of the neutron sensitivity and photon discrimination. The latter is usually achieved by setting a threshold higher than photon-induced signals or by difference/coincidence methods. The desired neutron energy response is typically sought using a combination of 6Li or 10B (n; a) radiators for slow neutrons, and polyethylene proton recoil radiators for neutrons up to a few MeV. Neutrons of higher energies produce detectable heavy charged recoils in the silicon diode itself. The Aloka PDM-313 model uses a single silicon diode with converters for fast and slow neutrons, and a filter for albedo neutrons [6]. The Fuji Electric EPD(NRN) uses four semiconductors, two for photons, one for thermal neutrons and one for fast neutrons, and performs a combination of their pulses [7]. The Saphydose-n, co-developed by IRSN and Saphymo, consists of a multi-strip
Table 1 Summary of characteristics of the electronic personal dosimeters available on the market Manufacturer and model
Type of sensor
Size (mm3)
Weight (g)
Dose range
Aloka PDM-313 Fuji electric EPD(NRN) Saphymo Saphydose-n Siemens EPD-N
One silicon detector, n sensitive Four silicon detectors, n=g sensitive One silicon strip detector, n sensitive Three silicon detectors, n=g sensitive
30 145 12 55 102 14.5 70 130 25 63 85 19
70 110 o200 110
10 mSv–0.1 Sv 100 mSv–1 Sv 1 mSv–1 Sv 10 mSv–16 Sv
F. d’Errico et al. / Nuclear Instruments and Methods in Physics Research A 505 (2003) 411–414
providing a sensitivity adequate for measurements at the radiation protection level [13]. Except for the Fuji Electric EPD, the response of all electronic personal dosimeters was investigated at PTB in Braunschweig with neutron beams from 24 keV up to 19 MeV, including the complete series of ISO-recommended energies [14]. In addition, some irradiations were performed with thermal neutrons at the research reactor in Geesthacht, Germany [15]. The neutron fluence of fast neutrons was measured by a recoil proton proportional counter and a recoil proton telescope with a standard uncertainty between 4.2% and 5.7%. The fluence of thermal neutrons was measured by a 3He-detector and time of flight spectrometry. The dosimeters were irradiated on a 30 cm 30 cm 15 cm PMMA slab and reference values of personal dose equivalent, Hp (10), were derived by multiplying the measured fluence of neutrons of the nominal energies with the fluenceto-personal dose equivalent conversion coefficient [16].
3. Results and discussion The results of our dose equivalent response measurements for neutrons are reported in Figs. 1 and 2, illustrating the results for commercial and laboratory EPDs, respectively. Fig. 1 indicates that the Aloka and Fuji Electric models both present a clear separation between the
Personal Dose Equivalent Response
silicon diode covered by two different polyethylene converters and by two 10B radiators, one in turn covered with Cd [8]. The more complex design allows for simplified signal processing. Finally, the Siemens EPD-N employs three semiconductordetectors, two for photons and one for neutrons. The latter is mainly sensitive to thermal and intermediate neutrons [9]. The laboratory devices under investigation comprise systems based on direct ion storage (DIS) chambers, silicon diodes, superheated drop detectors (SDD) and multicellular tissue equivalent proportional counters. The DIS device codeveloped by PSI Villigen, Switzerland, and RADOS is a MOSFET floating gate whose charge varies with the radiation-induced ionisation of an air chamber [10]. Various combinations of DIS elements with different ion chamber wall materials are tried in order to achieve, respectively, enhanced sensitivity to photons or neutrons. The neutron dose is determined by subtraction procedures. This is an extremely rugged device which operates well in relatively intense fields. The PTB dosimeter prototype consists of a single diode covered by 6LiF and polyethylene radiators [11]. In order to discriminate photons, only energy depositions higher than 1.5 MeV are accounted for. The signals of the diode are amplified and stored in a pulse height spectrum. A linear combination of the pulse height information in eight intervals of energy is used for the determination of the personal dose equivalent. The dosimeter co-developed by Yale and Pisa Universities, based on SDD, is an example of approach exploiting a radiation-induced phenomenon (bubble formation) inherently more probable at higher ionisation densities. The device comprises neutron sensor, acoustic bubble-counting electronics and a temperature-controller ensuring a stable and optimal response [12]. The counting electronics records bubble formation acoustically via a comparative pulse-shape analysis of ambient noise and detector signals. Finally, the IRSN-CIME is an example of the second basic approach to active neutron dosimetry, i.e., the use of LET spectrometry to weigh different radiation qualities rather than discriminating some radiation types. The device presents a large number of small detectors
413
10 2 10 1 10 0 10 -1 10 -2
ALOKA SIEMENS FUJI SAPHYDOSE
10 -3 thermal
10 -2 10 -1 10 0 Neutron Energy (MeV)
10 1
10 2
Fig. 1. Dose equivalent response of commercial EPDs.
F. d’Errico et al. / Nuclear Instruments and Methods in Physics Research A 505 (2003) 411–414
Personal Dose Equivalent Response
414 10 2 10 1
10 0
10 -1
10 -2
PSI-DIS PTB-DIODE YALE/PISA-SDD IRSN-CIME
thermal
10 -2 10 -1 10 0 Neutron Energy (MeV)
10 1
10 2
Fig. 2. Dose equivalent response of laboratory EPDs.
(n; a) capture reaction and the recoil proton regions. Between these two regions, in the range from 10 keV to 1 MeV which is very important for nuclear power plants, the Fuji Electric can underestimate the dose by as much as a factor of 100. The Aloka PDM-313 presents an excellent response down to 200 keV. However, in the epithermal energy range the dose is significantly overestimated, up to 80 times, before the albedo shield reduces the response at thermal energies. The Siemens EPD-N behaves like a typical thermal neutron dosimeter, and for fast neutrons the response is over two orders of magnitude too low. This requires appropriate calibration factors for each different exposure condition, which must be introduced by qualified operators using special software. Finally, the Saphydose-n presents an almost ideal response at all neutron energies, but reproducibility and fragility of the silicon strip detectors are a concern. Fragile devices are also the SDD and CIME dosimeter prototypes, whose response is also excellent at all neutron energies (Fig. 2). Extensive design engineering must be performed on these devices before they can be used in routine monitoring. Instead, ruggedness is a key advantage of the DIS device which also presents a good energy dependence of the response (results for a wall material with 2% LiNO3 are shown). The limiting factor in this case is the difficulty to achieve accurate neutron dose estimates within intense photon fields. Finally, the PTB singlediode prototype improves significantly on the
performance of devices with a comparably simple design; however, the response minimum around 1 MeV is a concern. This work is a first report on our extensive and systematic evaluation of different electronic personal dosimeters under identical testing conditions. One aspect that will be investigated with particular care is the directional dependence of their response. In fact, earlier studies in nuclear industry environments have shown that in the evaluation of personal dose equivalent the directional distribution of neutrons is actually even more important than their energy distribution [17]. A reported limitation to the EPD technology is the lack of wide dissemination of results of laboratory and field tests that have been performed [5]. These are mainly carried out at nuclear power plants and frequently lead to internal reports with limited public access. Addressing this problem is one of the purposes of this research. Acknowledgements This research was supported in part by EC contract FIKR-CT-2001-00175.
References [1] ICRP. Publication 60, Pergamon, Oxford, 1991. [2] C.R. Hirning, A.J. Waker, Radiat. Prot. Dosim. 70 (1–4) (1997) 67. [3] D.T. Bartlett, et al., Radiat. Prot. Dosim. 86 (2) (1999) 107. [4] W.G. Alberts, Radiat. Prot. Dosim. 85 (1–4) (1999) 21. [5] J. Shobe, K.L. Swinth, J. Res. NIST. 103 (1998) 421. [6] W.G. Alberts, et al., Radiat. Prot. Dosim. 51 (1994) 207. [7] K. Aoyama, et al., Proceedings of the 10th International IRPA Congress, CD-ROM, IRPA, Hiroshima, 2000. [8] T. Lahaye, et al., Radiat. Prot. Dosim. 96 (2001) 241. [9] Siemens Plc. 2000, in Technical Handbook, 2000. [10] A. Fiechtner, et al., Radiat. Prot. Dosim. 96 (2001) 269. [11] M. Luszik-Bhadra, Radiat. Prot. Dosim. 96 (2001) 227. [12] F. d’Errico, et al., Radiat. Prot. Dosim. 96 (2001) 261. [13] S. M!enard, et al., Radiat. Prot. Dosim. 96 (2001) 265. [14] S. Guldbakke, et al., Proceedings of the 26th Confernce . . 1994. Fachverband fur . Strahlenschutz, TUV-Verlag, Koln, . [15] R. Bottger, et al., GKSS Experimental Report, 2001. [16] ICRP. Publication 74, Pergamon, Oxford, 1997. [17] D.T. Bartlett, et al., Nucl. Instr. and Meth. A 476 (1–2) (2002) 386.
State of the art of electronic personal dosimeters for neutrons Francesco d’Erricoa,b,*, Marlies Luszik-Bhadrac, Thierry Lahayed a
Department of Therapeutic Radiology, Yale University School of Medicine, P.O. Box 208040, New Haven, CT 06520-8040, USA Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione (DIMNP), Universita" degli Studi di Pisa, Via Diotisalvi 2, I-56126 Pisa, Italy c Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, D-38116 Braunschweig, Germany d Institute for Protection and Nuclear Safety (IRSN), F 92265 Fontenay aux Roses Cedex, France
b
Abstract Despite a widely recognised need, electronic devices for personal dosimetry of neutrons or mixed neutron–photon fields are still far less established than systems for photon or beta radiations. A large research project is in progress to evaluate different methods currently used or under development for electronic personal dosimetry in mixed neutron– photon fields. The study includes testing in calibration fields as well as in representative workplaces of the nuclear industry. This paper describes the commercial and laboratory systems under investigation and their response characteristics. These were determined so far with measurements using ISO standard monoenergetic beams up to 19 MeV at the PTB in Braunschweig, Germany. r 2003 Published by Elsevier Science B.V. PACS: 87.53.PQ; 87.50.NP Keywords: Electronic personal dosimeters; monoenergetic neutron fields; Dose equivalent
1. Introduction A large number of electronic personal dosimeters for photon/beta radiations have been commercially available for several years and are currently being considered for primary dosimetry thanks to their high level of accuracy and reliability coupled with low detection limits. Conversely, electronic devices for personal dosimetry of neutrons or mixed neutron–photon fields
*Corresponding author. Department of Therapeutic Radiology, Yale University School of Medicine, P.O. Box 208040, New Haven, CT 06520-8040, USA. Tel.: +1-203-785-6679; fax: +1-203-737-4252. E-mail address: [email protected] (F. d’Errico).
are still far less established, despite a need which is widely recognised. In fact, increasing exposure levels are reported in the nuclear industry, deriving from more frequent in-service entries at commercial nuclear power plants, and from increased plant decommissioning and refurbishment activities. In addition, specific neutron exposures are increasing due to higher-burn up of fuel and to the use of mixed oxide elements. In recent years, a series of consensus requirements for neutron sensitive electronic personal dosimeters have been developed, mainly based on ICRP Publication 60 [1]. In particular, it has been suggested that the lower detection level should be 10 mSv (10 mSv/h, in ratemeter mode), dose increments should be in tens of microsievert, and the
0168-9002/03/$ - see front matter r 2003 Published by Elsevier Science B.V. doi:10.1016/S0168-9002(03)01110-0
412
F. d’Errico et al. / Nuclear Instruments and Methods in Physics Research A 505 (2003) 411–414
overall uncertainly on dose equivalent readings should not exceed a factor of 2 in any neutron spectrum [2–4]. In addition, criticality accidents such as the recent one in Tokai Mura, Japan, and a sustained military interest are behind the requirement that neutron EPDs should be capable of measuring high doses within short times [5], e.g., several Sievert per minute. More general requirements have also been expressed, such as availability of alarm functions, direct read out, computer interface, integration in monitoredaccess systems, battery charge allowing 100 h of continuous use and weight below 200 g. Addressing this demand, some neutron EPDs have appeared on the market in recent years. However, their development is a very difficult task, mainly because their physics, i.e. neutron interactions with matter, is much more complex than for photons and because a strongly variable energydependent quality factor must be folded into the detector response. In this framework, a research project sponsored by the European Commission has started to evaluate the relative merits of different methods for electronic personal dosimetry in mixed neutron–photon fields. The project includes investigations in standard calibration fields as well as in representative workplaces of the nuclear industry. This manuscript summarises the main characteristics of the commercial and laboratory systems under investigation and describes the dose equivalent response functions determined so far with measurements in reference neutron fields.
2. Materials and methods Three fundamental approaches can be identified for neutron electronic personal dosimetry. These
are based on: (a) using a physical or (bio)chemical effect with properties similar to the deposition of dose equivalent in tissue, (b) measuring LET spectra and folding them over the quality factor, and (c) designing a device with an energy dependence of the response resembling the fluence-to-dose equivalent conversion coefficient, hF ðEÞ: Most neutron EPDs, virtually all commercial ones, are based on the last method. However, two of the laboratory devices discussed hereafter follow the first two approaches. The commercial electronic personal dosimeters investigated in this work were: Aloka PDM-313, Fuji Electric EPD (NRN), Saphydose-n and Siemens EPD-N. Their main published characteristics are reported in Table 1. These devices are all based on semiconductor detectors, which are particularly attractive because of their ruggedness, small dimensions and limited cost. However, their use in neutron dosimetry poses two main problems: energy dependence of the neutron sensitivity and photon discrimination. The latter is usually achieved by setting a threshold higher than photon-induced signals or by difference/coincidence methods. The desired neutron energy response is typically sought using a combination of 6Li or 10B (n; a) radiators for slow neutrons, and polyethylene proton recoil radiators for neutrons up to a few MeV. Neutrons of higher energies produce detectable heavy charged recoils in the silicon diode itself. The Aloka PDM-313 model uses a single silicon diode with converters for fast and slow neutrons, and a filter for albedo neutrons [6]. The Fuji Electric EPD(NRN) uses four semiconductors, two for photons, one for thermal neutrons and one for fast neutrons, and performs a combination of their pulses [7]. The Saphydose-n, co-developed by IRSN and Saphymo, consists of a multi-strip
Table 1 Summary of characteristics of the electronic personal dosimeters available on the market Manufacturer and model
Type of sensor
Size (mm3)
Weight (g)
Dose range
Aloka PDM-313 Fuji electric EPD(NRN) Saphymo Saphydose-n Siemens EPD-N
One silicon detector, n sensitive Four silicon detectors, n=g sensitive One silicon strip detector, n sensitive Three silicon detectors, n=g sensitive
30 145 12 55 102 14.5 70 130 25 63 85 19
70 110 o200 110
10 mSv–0.1 Sv 100 mSv–1 Sv 1 mSv–1 Sv 10 mSv–16 Sv
F. d’Errico et al. / Nuclear Instruments and Methods in Physics Research A 505 (2003) 411–414
providing a sensitivity adequate for measurements at the radiation protection level [13]. Except for the Fuji Electric EPD, the response of all electronic personal dosimeters was investigated at PTB in Braunschweig with neutron beams from 24 keV up to 19 MeV, including the complete series of ISO-recommended energies [14]. In addition, some irradiations were performed with thermal neutrons at the research reactor in Geesthacht, Germany [15]. The neutron fluence of fast neutrons was measured by a recoil proton proportional counter and a recoil proton telescope with a standard uncertainty between 4.2% and 5.7%. The fluence of thermal neutrons was measured by a 3He-detector and time of flight spectrometry. The dosimeters were irradiated on a 30 cm 30 cm 15 cm PMMA slab and reference values of personal dose equivalent, Hp (10), were derived by multiplying the measured fluence of neutrons of the nominal energies with the fluenceto-personal dose equivalent conversion coefficient [16].
3. Results and discussion The results of our dose equivalent response measurements for neutrons are reported in Figs. 1 and 2, illustrating the results for commercial and laboratory EPDs, respectively. Fig. 1 indicates that the Aloka and Fuji Electric models both present a clear separation between the
Personal Dose Equivalent Response
silicon diode covered by two different polyethylene converters and by two 10B radiators, one in turn covered with Cd [8]. The more complex design allows for simplified signal processing. Finally, the Siemens EPD-N employs three semiconductordetectors, two for photons and one for neutrons. The latter is mainly sensitive to thermal and intermediate neutrons [9]. The laboratory devices under investigation comprise systems based on direct ion storage (DIS) chambers, silicon diodes, superheated drop detectors (SDD) and multicellular tissue equivalent proportional counters. The DIS device codeveloped by PSI Villigen, Switzerland, and RADOS is a MOSFET floating gate whose charge varies with the radiation-induced ionisation of an air chamber [10]. Various combinations of DIS elements with different ion chamber wall materials are tried in order to achieve, respectively, enhanced sensitivity to photons or neutrons. The neutron dose is determined by subtraction procedures. This is an extremely rugged device which operates well in relatively intense fields. The PTB dosimeter prototype consists of a single diode covered by 6LiF and polyethylene radiators [11]. In order to discriminate photons, only energy depositions higher than 1.5 MeV are accounted for. The signals of the diode are amplified and stored in a pulse height spectrum. A linear combination of the pulse height information in eight intervals of energy is used for the determination of the personal dose equivalent. The dosimeter co-developed by Yale and Pisa Universities, based on SDD, is an example of approach exploiting a radiation-induced phenomenon (bubble formation) inherently more probable at higher ionisation densities. The device comprises neutron sensor, acoustic bubble-counting electronics and a temperature-controller ensuring a stable and optimal response [12]. The counting electronics records bubble formation acoustically via a comparative pulse-shape analysis of ambient noise and detector signals. Finally, the IRSN-CIME is an example of the second basic approach to active neutron dosimetry, i.e., the use of LET spectrometry to weigh different radiation qualities rather than discriminating some radiation types. The device presents a large number of small detectors
413
10 2 10 1 10 0 10 -1 10 -2
ALOKA SIEMENS FUJI SAPHYDOSE
10 -3 thermal
10 -2 10 -1 10 0 Neutron Energy (MeV)
10 1
10 2
Fig. 1. Dose equivalent response of commercial EPDs.
F. d’Errico et al. / Nuclear Instruments and Methods in Physics Research A 505 (2003) 411–414
Personal Dose Equivalent Response
414 10 2 10 1
10 0
10 -1
10 -2
PSI-DIS PTB-DIODE YALE/PISA-SDD IRSN-CIME
thermal
10 -2 10 -1 10 0 Neutron Energy (MeV)
10 1
10 2
Fig. 2. Dose equivalent response of laboratory EPDs.
(n; a) capture reaction and the recoil proton regions. Between these two regions, in the range from 10 keV to 1 MeV which is very important for nuclear power plants, the Fuji Electric can underestimate the dose by as much as a factor of 100. The Aloka PDM-313 presents an excellent response down to 200 keV. However, in the epithermal energy range the dose is significantly overestimated, up to 80 times, before the albedo shield reduces the response at thermal energies. The Siemens EPD-N behaves like a typical thermal neutron dosimeter, and for fast neutrons the response is over two orders of magnitude too low. This requires appropriate calibration factors for each different exposure condition, which must be introduced by qualified operators using special software. Finally, the Saphydose-n presents an almost ideal response at all neutron energies, but reproducibility and fragility of the silicon strip detectors are a concern. Fragile devices are also the SDD and CIME dosimeter prototypes, whose response is also excellent at all neutron energies (Fig. 2). Extensive design engineering must be performed on these devices before they can be used in routine monitoring. Instead, ruggedness is a key advantage of the DIS device which also presents a good energy dependence of the response (results for a wall material with 2% LiNO3 are shown). The limiting factor in this case is the difficulty to achieve accurate neutron dose estimates within intense photon fields. Finally, the PTB singlediode prototype improves significantly on the
performance of devices with a comparably simple design; however, the response minimum around 1 MeV is a concern. This work is a first report on our extensive and systematic evaluation of different electronic personal dosimeters under identical testing conditions. One aspect that will be investigated with particular care is the directional dependence of their response. In fact, earlier studies in nuclear industry environments have shown that in the evaluation of personal dose equivalent the directional distribution of neutrons is actually even more important than their energy distribution [17]. A reported limitation to the EPD technology is the lack of wide dissemination of results of laboratory and field tests that have been performed [5]. These are mainly carried out at nuclear power plants and frequently lead to internal reports with limited public access. Addressing this problem is one of the purposes of this research. Acknowledgements This research was supported in part by EC contract FIKR-CT-2001-00175.
References [1] ICRP. Publication 60, Pergamon, Oxford, 1991. [2] C.R. Hirning, A.J. Waker, Radiat. Prot. Dosim. 70 (1–4) (1997) 67. [3] D.T. Bartlett, et al., Radiat. Prot. Dosim. 86 (2) (1999) 107. [4] W.G. Alberts, Radiat. Prot. Dosim. 85 (1–4) (1999) 21. [5] J. Shobe, K.L. Swinth, J. Res. NIST. 103 (1998) 421. [6] W.G. Alberts, et al., Radiat. Prot. Dosim. 51 (1994) 207. [7] K. Aoyama, et al., Proceedings of the 10th International IRPA Congress, CD-ROM, IRPA, Hiroshima, 2000. [8] T. Lahaye, et al., Radiat. Prot. Dosim. 96 (2001) 241. [9] Siemens Plc. 2000, in Technical Handbook, 2000. [10] A. Fiechtner, et al., Radiat. Prot. Dosim. 96 (2001) 269. [11] M. Luszik-Bhadra, Radiat. Prot. Dosim. 96 (2001) 227. [12] F. d’Errico, et al., Radiat. Prot. Dosim. 96 (2001) 261. [13] S. M!enard, et al., Radiat. Prot. Dosim. 96 (2001) 265. [14] S. Guldbakke, et al., Proceedings of the 26th Confernce . . 1994. Fachverband fur . Strahlenschutz, TUV-Verlag, Koln, . [15] R. Bottger, et al., GKSS Experimental Report, 2001. [16] ICRP. Publication 74, Pergamon, Oxford, 1997. [17] D.T. Bartlett, et al., Nucl. Instr. and Meth. A 476 (1–2) (2002) 386.